1. Field of the Invention
The present invention relates to serial link receivers, and more specifically related to receivers for high speed serial data transmissions.
2. Background of the Related Art
Computers and related telecommunications equipment use serial communications to send data in a sequence one bit at a time. Serial communications have come into wide use over long and short distances as a result of good signal integrity and high transmission speeds. For example, PCI Express (PCIe) is a popular computer expansion card standard that provides high speed serial communications. PCIe is used in many applications, including its use as a motherboard-level interconnect.
As the data rate increases in high speed serial data communications, the loss due to the capacitive load at the front end of the receiver increases and the bandwidth becomes limited. For different high speed low power communication standards, there is a wide input common mode range. The input common mode range of a conventional receiver is limited due to the direct connection of the amplifier to the input voltages, known as DC coupled connection. A small input common mode range limits the flexible combination of drivers and receivers made in different technologies. For some communication standards, AC coupled scheme is advantageous for filtering out low frequency noise and reducing input common mode level demand. However, it requires that the data signal be transmitted frequently between “1”s and “0”s. The receiver with AC coupled front end can not properly decode a signal which has a long consecutive string of “1”s and “0”s. For this type of the data pattern, a DC coupled front end is more appropriate.